1986 Nobel Prize in Physics(2)
Reason for Award
for their design of the scanning tunneling microscope
Laureates
West Germany
Switzerland
Explanation
Mr. Binnig and Mr. Rohrer invented a way of bringing an extremely sharp tip very close to a surface. When the gap is only a few atoms wide, electrons can tunnel across it, producing a tiny electric current. They kept this current constant while moving the tip, so the tip rose and fell following the surface. The recorded motion draws a map so detailed that individual atoms can be seen. This instrument is called a scanning tunneling microscope. It opened a brand-new window on the atomic world.
Related Keywords
Scanning tunneling microscope (STM)
An STM brings a conductive tip within a few angstroms of a surface and measures the quantum-tunneling current to create atomic-scale topographic maps. While raster-scanning, a feedback loop keeps the current constant, revealing height variations. Under vacuum or cryogenic conditions individual atoms are resolved. Varying the bias allows spectroscopy (STS) that probes the LDOS. The instrument is central to surface science and nanomaterials research.
Quantum tunneling effect
Quantum tunneling is the passage of a particle through an energy barrier it cannot classically cross, due to wavefunction penetration. In STM electrons tunnel across the vacuum barrier between tip and sample, producing current. The current depends exponentially on distance, changing by over an order of magnitude per ångström. This steep dependence is the key to atomic resolution. Tunneling is also vital in tunnel diodes and nuclear fusion theory.
Piezoelectric actuator
Piezoelectric actuators deform slightly when voltage is applied and move the STM tip with sub-nanometre precision. Their ability to extend or contract in ultra-fine steps enables atomic scanning. Because they generate charge under stress, they also act as sensors. Temperature drift and hysteresis demand careful calibration for high accuracy. Piezo devices are likewise used in MEMS, ultrasonic motors and many precision-positioning systems.
Atomic resolution
Atomic resolution is the capability to distinguish individual atoms. STM attains it thanks to the strong distance dependence of the tunnel current. Achieving it requires a single-atom tip apex and meticulous control of vibration and drift. Atomic resolution allows direct imaging of crystal defects and manipulation of single atoms. It has transformed both fundamental studies and nanofabrication.
Feedback loop
The STM feedback loop continuously adjusts the tip height to keep the tunnel current at a setpoint. PID control is common, and gain settings balance resolution with scan speed. An excessively fast loop oscillates, while a slow loop blurs images. Proper tuning is essential for high-quality data. Fast electronics now allow microsecond-scale response times.
Local density of states (LDOS)
The LDOS quantifies how many electronic states exist at a given energy and position. In STM the differential conductance dI/dV is proportional to the LDOS, allowing atomic-scale probing of electronic structure. It is essential for analysing band gaps, surface states and magnetic in-gap levels. In superconductors coherence peaks and quasiparticle interference patterns are visualised through LDOS mapping. LDOS is a central metric in nano-electronics and topological-matter research.